In the manufacture of blow molded thermoplastic articles, such as containers or the like, so-called "free extrusion" blow molding machines has long been utilized. Such machines typically issue a freely pendant, extruded tubular formation of plastic which is engaged by a mold closed on the tube immediately adjacent the orifice. The closure of the mold pinches the tube shut to form a blowable bubble. Typically, the mold-engaged, blowable bubble is moved away from the orifice, and the bubble is simply inflated or "blown" to the configuration of the blow mold.
While the type of operation is perfectly suitable for the manufacture of bottles or other containers of simple, essentially cylindrical shape, this method is ill adapted to the manufacture of handled containers, such as jugs, or the like. Such containers, generally, are large (on the order of one quart to one gallon in size) and the handle generally is located adjacent the shoulder of the container. To manufacture containers of this size on a free extrusion machine, the blowable bubble must be of sufficient size to be pinched shut by closure of the blow mold at the location of the handle. The extrusion of such a large tube necessarily results in the formation of large quantities of "flash" or waste material at the exterior of the blown shape. This flash (1) must be removed and reground at substantial expense, (2) requires either substantial hand labor or substantial trimming machine investment for its removal and (3) results in leakage from the container if improperly removed. All in all, substantial problems are involved in the manufacture of relatively large, handled containers from free extrusion blow molding machines, and such machines are not utilized for this purpose to any appreciable extent.
In my earlier filed U.S. application Ser. No. 103,624, filed Jan. 4, 1971, .Iadd.now U.S. Pat. No. 3,767,767 .Iaddend.I have proposed successively blow molding a freely extruded tubular parison into a preform and then into a final blown article. In this way, substantial process advantages are obtained, the formation of the pre-form conditions the thermoplastic material for maximum biaxial orientation during the final blowing step, and final blown articles of enhanced physical characteristics are obtained. Normally, such a process as described in my earlier application substantially uniformly expands the pre-form into the final container. However, in the manufacture of containers or other blown articles, such as handled bottles, it would be preferable to perform additional pre-form steps while the pre-form is in a condition most conducive to orientation, i.e. while the pre-form is at that temperaure at which orientation best occurs. Such additional pre-forming steps are carried out by the present invention.